Bidirectional buffers are known and are used in such programmable applications as FPGAs and other structures in which a signal on a line is to be amplified, but signal flow may be in either direction on the line. Prior art bidirectional buffers are known which comprise a pair of buffers connected to a line, in which one buffer amplifies in one direction and the other amplifier amplifies in the other direction. Control means then select the direction. Such a bidirectional buffer is described by Freeman in U.S. Reissue Patent Re 34,363 and shown in FIGS. 10a and 10b of that patent. Bidirectional buffers having only a single buffer element are described by Carter in U.S. Pat. Nos. 4,695,740 and 4,713,557. A three-state bidirectional buffer is described by Hsieh in U.S. Pat. No. 4,835,418. The above four patents are incorporated herein by reference.
In the integrated circuit industry, it is desirable to develop circuit structures which accomplish their purpose in the smallest possible space and operate at the highest possible speed.